1. Field of the Invention
This invention relates to autofocus cameras capable of alternating focus adjusting operations with releasing operations in continuous succession.
2. Description of the Related Art:
In the case of, while carrying out the focus adjusting (hereinafter described as AF) operation, continuously shooting a series of frames at a high speed, it is normal that the frame speed and the AF accuracy do not coincide. That is, the AF operation necessarily takes more than a certain time to perform. If this is perfectly completed for every one frame, the time necessary to shoot one frame gets longer. Conversely when priority is put on the frame speed, transition to the next shot occurs with the AF operation unfinished. Thus, the establishment of a sharp focus is not assured.
So, in the prior art, as shown in, for example, Japanese Laid-Open Patent Application No. Sho 57-146242, division into an AF priority mode and a frame speed priority mode is made to allow the photographer to take his choice.
But, this has the following drawbacks:
(i) To make a preferential choice of one of the sharp focus and the frame speed is to sacrifice the other. Nevertheless, the photographers generally desire a result that the degrees of priority of both are moderately well balanced. So, if, as has been described above, there are separate modes instead, they get lethargic in judging which is better to choose.
(ii) In the AF priority mode, the AF result is locked after the sharp focus is reached. Also, the condition of film transport and mechanical charge is monitored. When both have been completed, a releasing operation on the next frame is started. If, despite the completion of the AF operation in a short time, the film transport and mechanical charge is even still going on, it will take a considerably long time from after the AF is locked in sharp focus to the next shot. In other words, despite the AF priority mode, for a fast moving object, its image will probably be out of focus.
(iii) To another object which is moving at a faster speed, a problem arises that even if the AF operation alone is repeated, the camera cannot get out of the defocus state at all times, because there is a follow-up delay due to the time necessary to the AF operation. Since, in the AF priority mode, the shutter cannot be released until the sharp focus is reached, the shot cannot be taken indefinitely. In such a case, because shooting in the AF priority mode is impossible to do, provision must be made of, for example, a capability of automatic transition to a mode that, although the in-focus state is not perfect, the shutter can be released. Otherwise, a good shutter chance would be lost.